Niche occupancy of two (congeneric) skinks in an islands environment

Among the scincid lizards inhabiting the Mediterranean region, the Ocellated skink (Chalcides ocellatus) and the little-known and endangered Chafarinas' skink (Chalcides parallelus) co-occur in sympatry at the Chafarinas Islands (NW Africa). Although both species are present in the archipelago, C. ocellatus is spread in the three islands, but C. parallelus is present only in one island. What factors influence this distribution, and whether these two species show evidence for syntopy is unknown. In this study, we investigated spatial niche occupancy at the level of microhabitat of both skinks at the Chafarinas Islands. We tested for microhabitat differences between islands and then, we tested the null hypothesis of no differences between microhabitat used by each of these skink species and a set of locations chosen at random from the general habitat. Results showed that the distribution and abundance of available microhabitats were different among islands, thus each island has different spatial niches that may be important in distinguishing the areas occupied by these skinks. Results also revealed that C. ocellatus did not use available microhabitats at random, but preferentially selected particular microhabitats. However, C. parallelus used microhabitats according to their availability, although it showed some aspects of habitat selection similar to C. ocellatus. Our results showed that the inclusion of detailed microhabitat descriptors could be useful for understanding patterns of niche occupancy by these skinks species. Furthermore, to our knowledge this is the first study documenting the spatial niche selection of C. parallelus and provides novel ecological information that may be of major importance to develop management strategies that will help to conserve this endangered species.